Relative bioavailability of four controlled-release nifedipine products.

Four controlled-release nifedipine products were investigated in two clinical studies. In study 1, 22 healthy male volunteers took part in an open, multiple-dose, randomized, crossover study to determine the relative bioavailability of two 10 mg controlled-release nifedipine tablets (Adalat Retard, Bayer), administered 12 hourly, and one 20 mg controlled-release nifedipine tablet (Adalat Retard, Bayer) administered 12 hourly. In study 2, 24 healthy male volunteers took part in an open, multiple-dose, randomized, three-period, crossover study to determine the relative bioavailability of (i) two 30 mg nifedipine gastro-intestinal therapeutic system (GITS) tablets (Adalat XL, Bayer) administered once daily; (ii) one 60 mg nifedipine GITS tablet (Adalat XL, Bayer) administered once daily; and (iii) one 20 mg plus one 10 mg nifedipine controlled-release tablet (Adalat Retard, Bayer), administered 12 hourly. In both studies detailed pharmacokinetic data, in particular with respect to the controlled-release characteristics of the different formulations, were collected. Results of both studies indicate that all nifedipine products investigated are bioequivalent with respect to the extent of absorption of nifedipine. The nifedipine GITS products (Adalat XL) have better controlled-release properties than the Adalat Retard product, and are suitable for once-a-day administration.